RTK vs PPK vs DGNSS

Why GNSS Needs Corrections

A receiver computes its position from the time satellite signals take to arrive. That timing is degraded by predictable error sources — the ionosphere and troposphere bending the signal, small satellite clock and orbit errors, and signal multipath. Acting alone, a receiver can only get within a few meters.

The fix is differential positioning: place a second receiver — the base station — on a point whose coordinates are already known. Because the base sees the same errors as a nearby rover, it can measure them and broadcast a correction. The rover applies that correction and collapses most of the shared error. The three techniques below are just different ways of generating and applying that correction.

DGNSS — Differential GNSS

DGNSS uses the code (pseudorange) measurement — the same coarse measurement a standalone receiver uses, but corrected by the base. The base computes how far off each satellite’s range is and broadcasts those corrections; the rover applies them in real time.

• Accuracy: typically sub-meter to a few decimeters.
• Strengths: simple, robust, quick to converge, tolerant of weaker signal conditions.
• Use it for: GIS data collection, asset mapping, navigation — jobs where decimeter accuracy is plenty.

RTK — Real-Time Kinematic

RTK steps up to the carrier phase — measuring the GNSS signal’s wavelength (about 19 cm for GPS L1) rather than its code. By resolving how many whole wavelengths lie between satellite and receiver (the “integer ambiguity”), RTK reaches centimeter accuracy. The base streams corrections to the rover over a live data link — radio, cellular, or the internet (see NTRIP).

• Accuracy: roughly 1–2 cm horizontal once the rover reports a Fixed solution.
• Strengths: survey-grade results in the field, right now — you stake out and verify on the spot.
• Watch out for: it depends on a reliable, low-latency link; lose the link or drop to a Float solution and accuracy degrades immediately.

PPK — Post-Processed Kinematic

PPK uses the exact same carrier-phase math as RTK, but nothing is corrected in the field. Instead, the base and the rover each independently log their raw observations. Back at the office, the two logs are combined and processed together to compute the corrected trajectory.

• Accuracy: centimeter — on par with RTK, often slightly better because processing can run both forward and backward in time and reject bad epochs.
• Strengths: no live data link needed — ideal where radio/cell coverage is poor, or on fast-moving platforms like drones where a dropped link would ruin an RTK flight.
• Trade-off: you don’t see results until post-processing, so you can’t stake out or catch problems on site.

Side by Side

Which Should You Use?

• Need only decimeter accuracy, or working in tough signal conditions? DGNSS.
• Need centimeter accuracy and to act on it in the field — staking points, verifying as you go — with a solid data link? RTK.
• Need centimeter accuracy but the link is unreliable, or you’re flying a drone / mapping at speed? PPK.

Many modern workflows hedge with RTK + PPK together: run RTK live for on-site feedback, but also log raw data so the trajectory can be re-derived by PPK if the link drops — the best of both.